Polyester bottle resins having reduced frictional properties and methods for making the same

ABSTRACT

The invention is a polyester resin that includes between about 20 and 200 ppm of an inert particulate additive, preferably selected from the group consisting of surface-modified talc and surface-modified calcium carbonate. The invention is also a method of making the polyester resin, which is capable of being formed into low-haze, high-clarity bottles possessing reduced coefficient of friction.

[0001] CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application incorporates entirely by reference co-pendingand commonly-assigned application Ser. No. ______ for Methods ofPost-Polymerization Injection in Continuous Polyethylene TerephthalateProduction.

FIELD OF THE INVENTION

[0003] The invention relates to a polyester resin that includes smallamounts of an inert particulate additive, which reduces the coefficientof friction in bottles formed from the polyester resin while maintainingbottle clarity.

BACKGROUND OF THE INVENTION

[0004] Polyester resins, especially polyethylene terephthalate (PET) andits copolyesters, are widely used to produce rigid packaging, such astwo-liter soft drink containers. Polyester packages produced bystretch-blow molding possess high strength and shatter resistance, andhave excellent gas barrier and organoleptic properties as well.Consequently, such plastics have virtually replaced glass in packagingnumerous consumer products (e.g., carbonated soft drinks, fruit juices,and peanut butter).

[0005] In conventional techniques of making bottle resin, modifiedpolyethylene terephthalate is polymerized in the melt phase to anintrinsic viscosity of about 0.6 deciliters per gram (dl/g), whereuponit is polymerized in the solid phase to achieve an intrinsic viscositythat better promotes bottle formation. Before 1965, the only feasiblemethod of producing polyethylene terephthalate polyester was to usedimethyl terephthalate (DMT). In this technique, dimethyl terephthalateand ethylene glycol are reacted in a catalyzed ester interchangereaction to form bis(2-hydroxyethyl)terephthalate monomers andoligomers, as well as a methanol byproduct that is continuously removed.These bis(2-hydroxyethyl)terephthalate monomers and oligomers are thencatalytically polymerized via polycondensation to produce polyethyleneterephthalate polymers.

[0006] Purer forms of terephthalic acid (TA) are now increasinglyavailable. Consequently, terephthalic acid has become an acceptable, ifnot preferred, alternative to dimethyl terephthalate as a startingmaterial for the production of polyethylene terephthalate. In thisalternative technique, terephthalic acid and ethylene glycol react in agenerally uncatalyzed esterification reaction to yield low molecularweight monomers and oligomers, as well as a water byproduct that iscontinuously removed. As with the dimethyl terephthalate technique, themonomers and oligomers are subsequently catalytically polymerized bypolycondensation to form polyethylene terephthalate polyester. Theresulting polyethylene terephthalate polymer is substantially identicalto the polyethylene terephthalate polymer resulting from dimethylterephthalate, albeit with some end group differences.

[0007] Polyethylene terephthalate polyester may be produced in a batchprocess, where the product of the ester interchange or esterificationreaction is formed in one vessel and then transferred to a second vesselfor polymerization. Generally, the second vessel is agitated and thepolymerization reaction is continued until the power used by theagitator reaches a level indicating that the polyester melt has achievedthe desired intrinsic viscosity and, thus, the desired molecular weight.More commercially practicable, however, is to carry out theesterification or ester interchange reactions, and then thepolymerization reaction as a continuous process. The continuousproduction of polyethylene terephthalate results in greater throughput,and so is more typical in large-scale manufacturing facilities.

[0008] When the polymerization process is complete, the resultingpolymer melt is typically extruded and pelletized for convenient storageand transportation. Thereafter, the polyethylene terephthalate may bemolded into preforms and bottles.

[0009] As will be understood by those having ordinary skill in the art,polyethylene terephthalate is typically converted into a container via atwo-step process. First, an amorphous bottle preform is produced frombottle resin by melting the resin in an extruder and injection moldingthe molten polyester into a preform. Such a preform usually has anoutside surface area that is at least an order of magnitude smaller thanthe outside surface of the final container. The preform is reheated toan orientation temperature that is typically 30° C. above the glasstransition temperature. The reheated preform is then placed into abottle mold and, by stretching and inflating with high-pressure air,formed into a bottle. Those of ordinary skill in the art will understandthat any defect in the preform is typically transferred to the bottle.Accordingly, the quality of the bottle resin used to forminjection-molded preforms is critical to achieving commerciallyacceptable bottles.

[0010] Polyethylene terephthalate bottles, especially straight-walledtwo-liter soft drink bottles, often possess high coefficients offriction (COF). This is a significant problem in the bottling industryas excessive friction between adjacent bottles prevents such bottlesfrom easily and efficiently sliding past one another as they aredepalletized. To improve depalletizing, bottlers conventionally resortto water misting and line lubrication on a filling line.

[0011] Therefore, there is a need for a polyester bottle that possessesreduced coefficient of friction while retaining bottle clarity.

OBJECT AND SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the present invention to providea high-clarity polyester bottle including a surface-modified talc orsurface-modified calcium carbonate in concentrations that permit thebottle to possess reduced coefficient of friction.

[0013] It is a further object of the present invention to provide amethod for making polyethylene terephthalate preforms and bottlespossessing reduced coefficients of friction.

[0014] It is a further object of the present invention to provide apolyester resin that is capable of being formed into high-claritybottles possessing reduced coefficient of friction.

[0015] It is a further object of the present invention to provide amethod for making polyethylene terephthalate resin that can be formedinto high-clarity bottles possessing reduced coefficient of friction.

[0016] The foregoing, as well as other objectives and advantages of theinvention and the manner in which the same are accomplished, is furtherspecified within the following detailed description and its accompanyingdrawings.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 illustrates the qualitative effect on bottle sidewall hazeand friction as a function of increasing concentration of the reducedCOF additive.

[0019]FIGS. 2 and 3 illustrate the theoretical loss of intrinsicviscosity of polyethylene terephthalate as a function of theconcentration of a reactive (additive) carrier at various molecularweights.

DETAILED DESCRIPTION

[0020] In one aspect, the invention is a polyester resin that is capableof being formed into low-haze, high-clarity bottles possessing reducedcoefficient of friction. The bottle resin is characterized by theinclusion of between about 20 and 200 ppm of an inert particulateadditive, preferably either talc (i.e., a natural hydrous magnesiumsilicate of representative formula 3MgO.4SiO₂.H₂O)or precipitatedcalcium carbonate, having an average particle size of less than aboutten microns, more preferably less than two microns. The inertparticulate additive, which is preferably surface-treated, is present inlow concentrations to ensure that bottles formed from the polyesterbottle resin possess low haziness. Such improved frictionalcharacteristics reduce, and can eliminate, the need to apply, duringfilling operation, external lubricants to the surfaces of containersformed from the present polyester resin.

[0021] Preferably, the polyester resin includes between about 40 and 150ppm of the inert particulate additive, more preferably between about 40and 100 ppm of the inert particulate additive, and most preferablybetween about 60 and 100 ppm of the inert particulate additive.

[0022] In another aspect, the invention is a method for making apolyester resin that can be formed into high-clarity bottles possessingreduced coefficient of friction. The method generally includes reactinga terephthalate component and a diol component to form polyethyleneterephthalate precursors, e.g., bis(2-hydroxyethyl) terephthalate, whichare then polymerized via melt phase polycondensation to form polymers ofpolyethylene terephthalate of a desired molecular weight. Duringpolycondensation, which is usually enhanced by catalysts, ethyleneglycol is continuously removed to create favorable reaction kinetics.The method is characterized by the introduction of between about 20 and200 ppm of an inert particulate additive-more preferably talc or calciumcarbonate in the aforementioned concentration ranges-that is capable ofreducing the coefficient of friction in bottles formed from thepolyethylene terephthalate polymers. As noted, the friction-reducingadditive has an average particle size of less than about ten microns andis preferably either surface-modified talc or surface-modified calciumcarbonate.

[0023] Without being bound to a particular theory, it is believed thatthe introduction of fillers can create discontinuous phases within thepolyethylene terephthalate resin. During stretch-blow molding, suchdiscontinuities lead to the formation of microvoids around the fillerparticles. This causes bottle haze because of differences in refractiveindex between the microvoid regions and the polyethylene terephthalatematrix. The microvoids are apparently caused by an inherentincompatibility of the filler particles with the polyethyleneterephthalate matrix.

[0024] According to the present invention, to improve compatibilitybetween the polyethylene terephthalate polymers and the inertparticulate additive, the inert particulate additive is preferablytreated with a coupling agent before its addition to polyethyleneterephthalate polymers. This has been found to significantly reducebottle haze while reducing bottle COF. Without coupling agent treatment,the polyethylene terephthalate polymers resist wetting of the inertparticles. Thus, all things being equal, surface treatment reducespolyester bottle haze.

[0025] Accordingly, the inert particulate additive is preferablysurface-modified talc or surface-modified calcium carbonate. Inparticular, talc is preferably surface treated using silanes, especiallyorganosilanes such as 3-aminopropyl trimethoxy silane and 3-aminopropyltriethoxy silane, at a loading of between about 0.5 and one weightpercent. Calcium carbonate is preferably surface treated using stearicacid at a loading of between about one and two weight percent. Treatmentwith these coupling agents (e.g., organosilane and stearic acid)facilitates compatibility between the inert particles and thepolyethylene terephthalate polymer by introducing covalent chemicalbonding between the particle surface and the polyethylene terephthalatepolymer, or by introducing a hydrophobic moiety that is compatible withthe polyethylene terephthalate to facilitate better polymer wetting ofthe particle.

[0026] The inclusion of an inert particulate additive in thepolyethylene terephthalate resin reduces bottle friction, but alsoincreases bottle haze. FIG. 1 depicts the trade-off between reducedfriction and haze. In brief, concentrations of talc or calcium carbonategreater than about 200 ppm (and in some instances even 100 ppm) willresult in unacceptable hazy bottles, and concentrations of talc orcalcium carbonate much less than about 20 ppm will not noticeably reducebottle COF. As described previously, the polyester resin preferablyincludes between about 40 and 150 ppm of the inert particulate additiveand most preferably between about 60 and 100 ppm of the inertparticulate additive.

[0027] The efficacy of the present invention is demonstrated by testingthat shows the addition of 100 ppm of surface-treated talc reducescoefficient of friction by about 90 percent, as measured using ASTM Testmethod D 1894.

[0028] Note that at any given weight fraction of inert particulateadditive, increasing particle size will exacerbate haziness with noconcomitant reduction in friction. An average particle size of much morethan ten microns generally causes unacceptable bottle haze. As will beunderstood by those familiar with this art, particle size is typicallymeasured by techniques based on light scattering. Particle sizes anddistributions are often characterized using a Hegman Fineness numberdetermined from ASTM D1210-79.

[0029] As used herein, the term “diol component” refers primarily toethylene glycol, although other diols (e.g., polyethylene glycol) may beused as well. It will be understood by those of ordinary skill in theart that the diol component usually forms the majority of terminal endsof the polymer chains and so is present in the composition in slightlygreater fractions. For example, the molar ratio of the terephthalatecomponent and the diol component is typically between about 1.0:1.0 and1.0:1.6.

[0030] As used herein, the term “terephthalate component” refers todiacids and diesters that can be used to prepare polyethyleneterephthalate. In particular, the terephthalate component mostlyincludes terephthalic acid and dimethyl terephthalate, but can includediacid and diester comonomers as well. In this regard, those havingordinary skill in the art will know that there are two conventionalmethods for forming polyethylene terephthalate. These methods are wellknown to those skilled in the art.

[0031] One method employs a direct esterification reaction usingterephthalic acid and excess ethylene glycol. In this technique, theaforementioned step of reacting a terephthalate component and a diolcomponent includes reacting terephthalic acid and ethylene glycol in aheated esterification reaction to form monomers and oligomers ofterephthalic acid and ethylene glycol, as well as a water byproduct. Toenable the esterification reaction to go essentially to completion, thewater must be continuously removed as it is formed.

[0032] The other method involves a two-step ester exchange reaction andpolymerization using dimethyl terephthalate and excess ethylene glycol.In this technique, the aforementioned step of reacting a terephthalatecomponent and a diol component includes reacting dimethyl terephthalateand ethylene glycol in a heated ester exchange reaction to form monomersand oligomers of terephthalate and ethylene glycol, as well as methanolas a byproduct. To enable the ester exchange reaction to go essentiallyto completion, the methanol must be continuously removed as it isformed.

[0033] It will be understood by those having ordinary skill in the artthat the polyethylene terephthalate herein described may be a modifiedpolyethylene terephthalate to the extent the diol component can includeother glycols besides ethylene glycol (e.g., diethylene glycol,1,3-propanediol, 1,4-butanediol and 1,4-cyclohexane dimethanol), and theterephthalate component includes modifiers such as isophthalic acid,2,6-naphthalene dicarboxylic acid, succinic acid, or one or morefunctional derivatives of terephthalic acid. In fact, most commercialpolyethylene terephthalate polymers are modified polyethyleneterephthalate polyesters.

[0034] An advantage of the present invention is that the inertparticulate additives may be added to any polyester bottle resinformulation to reduce COF in bottles made therefrom. In this regard,bottle grade polyester resins will not be discussed herein in detail assuch resins are well known in the art. For example, commonly-assigned,co-pending application Ser. No. 09/456,253 filed Dec. 7, 1999, for aMethod of Preparing Modified Polyester Bottle Resins, which discussesseveral U.S. patents that disclose various modified polyethyleneterephthalate resins. This application is hereby incorporated entirelyherein by reference.

[0035] While the present application is directed to polyester resins, itis believed that non-polyester resins, such as high-density polyethylene(HDPE), low-density polyethylene (LDPE), linear low-density polyethylene(LLDPE), polyvinyl chloride (PVC), and polyvinyl chloride (PVDC), whichare typically used in films, show analogous frictional characteristicsand thus benefit from the use of inert particulate additives to reduceCOF.

[0036] In the present invention, the direct esterification reaction ispreferred over the older, two-step ester exchange reaction. As noted,the direct esterification technique reacts terephthalic acid andethylene glycol to form low molecular weight monomers, oligomers, andwater.

[0037] For example, in a typical, exemplary process the continuous feedenters a direct esterification vessel that is operated at a temperatureof between about 240° C. and 290° C. and at a pressure of between about5 and 85 psia for between about one and five hours. The reaction, whichis typically uncatalyzed, forms low molecular weight monomers,oligomers, and water. The water is removed as the esterificationreaction proceeds to drive a favorable reaction equilibrium.

[0038] Thereafter, the low molecular weight monomers and oligomers arepolymerized via polycondensation to form polyethylene terephthalatepolyester. This polycondensation stage generally employs a series of twoor more vessels and is operated at a temperature of between about 250°C. and 305° C. for between about one and four hours. Thepolycondensation reaction usually begins in a first vessel called thelow polymerizer. The low polymerizer is operated at a pressure range ofbetween about 0 and 70 torr. The monomers and oligomers polycondense toform polyethylene terephthalate and ethylene glycol.

[0039] The ethylene glycol is removed from the polymer melt using anapplied vacuum to drive the reaction to completion. In this regard, thepolymer melt is typically agitated to promote the escape of the ethyleneglycol from the polymer melt and to assist the highly viscous polymermelt in moving through the polymerization vessel.

[0040] As the polymer melt is fed into successive vessels, the molecularweight and thus the intrinsic viscosity of the polymer melt increases.The temperature of each vessel is generally increased and the pressuredecreased to allow greater polymerization in each successive vessel.

[0041] The final vessel, generally called the “high polymerizer,” isoperated at a pressure of between about 0 and 40 torr. Like the lowpolymerizer, each of the polymerization vessels is connected to a flashvessel and each is typically agitated to facilitate the removal ofethylene glycol. The residence time in the polymerization vessels andthe feed rate of the ethylene glycol and terephthalic acid into thecontinuous process is determined in part based on the target molecularweight of the polyethylene terephthalate polyester. Because themolecular weight can be readily determined based on the intrinsicviscosity of the polymer melt, the intrinsic viscosity of the polymermelt is generally used to determine the feed rate of the reactants andthe residence time within the polymerization vessels.

[0042] Note that in addition to the formation of polyethyleneterephthalate polymers, side reactions occur that produce undesirableby-products. For example, the esterification of ethylene glycol formsdiethylene glycol (DEG), which is incorporated into the polymer chain.As is known to those of skill in the art, diethylene glycol lowers thesoftening point of the polymer. Moreover, cyclic oligomers (e.g., trimerand tetramers of terephthalic acid and ethylene glycol) may occur inminor amounts. The continued removal of ethylene glycol as it forms inthe polycondensation reaction will generally reduce the formation ofthese by-products.

[0043] After the polymer melt exits the polycondensation stage,typically from the high polymerizer, it is generally filtered andextruded, preferably immediately after exiting the polycondensationstage. After extrusion, the polyethylene terephthalate is quenched,preferably by spraying with water, to solidify it. The solidifiedpolyethylene terephthalate polyester is cut into chips or pellets forstorage and handling purposes. As used herein, the term “pellets” isused generally to refer to chips, pellets, and the like.

[0044] As will be known to those of skill in the art, the pellets formedfrom the polyethylene terephthalate polymers and the reactive carriermay be subjected to crystallization followed by solid statepolymerization (SSP) to increase the molecular weight of thepolyethylene terephthalate resin. It should be noted that the method ofthe invention does not adversely affect the SSP rate and often will evenincrease the SSP rate. The polyester chips are then re-melted andre-extruded to form bottle preforms, which can thereafter be formed intopolyester containers (e.g., beverage bottles). The levels of inertparticulate additives (i.e., less than 200 ppm) do not significantlyaffect cycle times during injection molding operations.

[0045] Although the prior discussion assumes a continuous productionprocess, it will be understood that the invention is not so limited. Theteachings disclosed herein may be applied to semi-continuous processesand even batch processes.

[0046] The inert particulate additives herein disclosed can beintroduced to the polyethylene terephthalate polymers as a powder, as aconcentrate in polyethylene terephthalate, or as a concentrate in aliquid carrier. The preferred point of addition in the polyethyleneterephthalate polymerization process is after completion ofpolycondensation (i.e., mixed with the molten polymer stream after thefinal polymerization vessel).

[0047] In one embodiment, the method introduces an essentially dry,inert particulate additive into the polyethylene terephthalate polymersduring or after the polycondensation stage. Dry, inert particulateadditive may be introduced via a split-stream method, such as thatdisclosed by U.S. Pat. No. 5,376,702 for a Process and Apparatus for theDirect and Continuous Modification of Polymer Melts. This patentdiscloses dividing a polymer melt stream into an unmodified stream and abranch stream that receives additives. In particular, a side streamtakes a portion of the branch stream to an extruder, where additives areintroduced. Unfortunately, this kind of technique is not onlycomplicated, but also costly, requiring at least a screw extruder andadditional melt piping to process additives. Consequently, sucharrangements are inconvenient and even impractical where total additiveconcentrations are low (e.g., less than one weight percent).

[0048] Most preferably, the inert particulate additives are added afterthe melt polymerization is complete. Such late addition is desirablebecause esterification and polycondensation conditions can cause acalcium carbonate additive to dissolve in the polymer, which destroysits particulate nature. Consequently, calcium carbonate is preferablyadded to the polyethylene terephthalate polymer before extrusion andpelletization.

[0049] Similarly, high polycondensation temperatures can strip couplingagents (e.g., silane surface treatment) from talc. As talc is notsusceptible to dissolution in the polymer, its addition is moreadaptable than is the addition of calcium carbonate (i.e., talc itselfcan be added at any point during the polymerization).

[0050] Accordingly, in a preferred embodiment, the method introduces theinert particulate additive via a reactive carrier, rather than an inertcarrier or no carrier at all. The reactive carrier, which preferably hasa molecular weight of less than about 10,000 g/mol may be introducedduring polycondensation, or more preferably, after the polycondensationis complete. In either respect, the reactive carrier should beintroduced to the polyethylene terephthalate polymers in quantities suchthat bulk polymer properties are not significantly affected.

[0051] Most preferably, the reactive carrier has a melting point thatensures that it is a liquid or slurry at near ambient temperatures. Nearambient temperatures not only simplify the unit operations (e.g.,extruders, heaters, and piping), but also minimize degradation of theinert particulate additives. As used herein, the term “near ambient”includes temperatures between about 20° C. and 60° C.

[0052] As a general matter, the reactive carrier should make up no morethan about one weight percent of the polyethylene terephthalate resin.Preferably, the reactive carrier is introduced to the polyethyleneterephthalate polymers in quantities such that its concentration in thepolymer resin is less than about 1000 ppm (i.e., 0.1 weight percent).Reducing the reactive carrier to quantities such that its concentrationin the polymer resin is less than 500 ppm (i.e., 0.05 weight percent)will further reduce potential adverse effects to bulk polymerproperties.

[0053] In general, reactive carriers having carboxyl, hydroxyl, or aminefunctional groups are favored. Preferred are polyols, especiallypolyester polyols and polyether polyols, having a molecular weight thatis sufficiently high such that the polyol will not substantially reducethe intrinsic viscosity of the polyethylene terephthalate polymer, and aviscosity that facilitates pumping of the polyol. Polyethylene glycol isa preferred polyol. Other exemplary polyols include functionalpolyethers, such as polypropylene glycol that is prepared from propyleneoxide, random and block copolymers of ethylene oxide and propyleneoxide, and polytetramethylene glycol that is derived from thepolymerization of tetrahydrofuran.

[0054] Alternatively, the reactive carrier may include dimer or trimeracids and anhydrides. In another embodiment, the reactive carrier maypossess, in addition to or in place of terminal functional groups,internal functional groups (e.g., esters, amides, and anhydrides) thatreact with the polyethylene terephthalate polymers. In yet anotherembodiment, the reactive carrier may include non-functional esters,amides, or anhydrides that is capable of reacting into the polyethyleneterephthalate polymers during solid state polymerization and that willnot cause the polyethylene terephthalate polymers to suffer intrinsicviscosity loss during injection molding processes.

[0055] In view of the foregoing, a preferred embodiment of the inventionincludes reacting terephthalic acid and ethylene glycol in a heatedesterification reaction to form monomers and oligomers of terephthalicacid and ethylene glycol, then polymerizing these monomers and oligomersvia melt phase polycondensation to form polyethylene terephthalatepolymers. Thereafter, between about 20 and 200 ppm of eithersurface-modified talc or surface-modified calcium carbonate isintroduced into the polyethylene terephthalate polymers using a reactivecarrier, which facilitates uniform blending within the polymer melt.Preferably, the reactive carrier is a polyol (e.g., polyethylene glycol)having a molecular weight that permits the polyol to be pumped at nearambient temperatures (e.g., less than 60° C.) and that is introduced tothe polyethylene terephthalate polymers in quantities such that bulkproperties of the polyethylene terephthalate polymers are notsignificantly affected. The polyethylene terephthalate polymers are thenformed into chips (or pellets via a polymer cutter) before being solidstate polymerized. Importantly, the polyol reactive carrier combineswith the polyethylene terephthalate polymer such that it isnon-extractable during subsequent processing operations (e.g., formingpolyester preforms or beverage containers).

[0056] As will be understood by those of ordinary skill in the art,macromolecules are considered to be polymers at an intrinsic viscosityof about 0.45 dl/g. This roughly translates to a molecular weight of atleast about 13,000 g/mol. In contrast, the reactive carriers accordingto the present invention have molecular weights that are less than about10,000 g/mol. The molecular weight of the reactive carrier is typicallyless than 6000 g/mol, preferably less than 4000 g/mol, more preferablybetween about 300 and 2000 g/mol, and most preferably between about 400and 1000 g/mol. As used herein, molecular weight refers tonumber-average molecular weight, rather than weight-average molecularweight.

[0057]FIGS. 2 and 3 illustrate the theoretical loss of intrinsicviscosity as a function of reactive carrier concentration at severalmolecular weights. FIG. 2 depicts the impact of the reactive carrier onupon polyethylene terephthalate having an intrinsic viscosity of 0.63dl/g. Similarly, FIG. 3 depicts the impact of the reactive carrier onupon polyethylene terephthalate having intrinsic viscosity of 0.45 dl/g.Note that at any concentration, the reactive carriers having highermolecular weights have less adverse effect upon intrinsic viscosity ofthe polymer resin.

[0058] As used herein, the term “intrinsic viscosity” is the ratio ofthe specific viscosity of a polymer solution of known concentration tothe concentration of solute, extrapolated to zero concentration.Intrinsic viscosity, which is widely recognized as standard measurementsof polymer characteristics, is directly proportional to average polymermolecular weight. See, e.g., Dictionary of Fiber and Textile Technology,Hoechst Celanese Corporation (1990); Tortora & Merkel, Fairchild'sDictionary of Textiles (7^(th) Edition 1996).

[0059] Intrinsic viscosity can be measured and determined without undueexperimentation by those of ordinary skill in this art. For theintrinsic viscosity values described herein, the intrinsic viscosity isdetermined by dissolving the copolyester in orthochlorophenol (OCP),measuring the relative viscosity of the solution using a SchottAutoviscometer (AVS Schott and AVS 500 Viscosystem), and thencalculating the intrinsic viscosity based on the relative viscosity.See, e.g., Dictionary of Fiber and Textile Technology (“intrinsicviscosity”).

[0060] In particular, a 0.6-gram sample (+/−0.005 g) of dried polymersample is dissolved in about 50 ml (61.0-63.5 grams) oforthochlorophenol at a temperature of about 105° C. Fiber and yarnsamples are typically cut into small pieces, whereas chip samples areground. After cooling to room temperature, the solution is placed in theviscometer and the relative viscosity is measured. As noted, intrinsicviscosity is calculated from relative viscosity.

[0061] Finally, as is understood by those familiar with polyesterpackaging, ultraviolet (UV) radiation absorbers protect polymers and thecontents of packages formed from the same. Where UV absorbers are addedto the bottle resin during the injection molding process, there is atendency for such UV absorbers (and when used, reactive carriers thatdeliver UV absorbers) to leave deposits in the injection molds used forpreforms. Such deposits cause the preforms to stick in the injectionmolds slightly longer, thereby slowing preform manufacturing efficiency.

[0062] Without being bound to any particular theory, it is believed thatthe interaction between a UV absorber and the bottle resin producesbyproducts that in turn deposit on the molds in which polyester bottlepreforms are manufactured. These deposits cause the preforms to stick inthe mold, thereby slowing the production rate of the preform-makingprocess. Calcium carbonate, and especially talc, have been found to havethe beneficial effect of reducing adherence to preform molds, therebyincreasing the speed and efficiency of the injection molding process.Accordingly, an embodiment of the polyester resin includes both an inertparticulate additive as herein described and a UV absorber.

[0063] In the drawings and the specification, typical embodiments of theinvention have been disclosed. Specific terms have been used only in ageneric and descriptive sense, and not for purposes of limitation. Thescope of the invention is set forth in the following claims.

That which is claimed is:
 1. A polyester resin that is capable of beingformed into high-clarity bottles possessing reduced coefficient offriction, the resin comprising polyethylene terephthalate and betweenabout 20 and 200 ppm of an inert particulate additive selected from thegroup consisting of talc and calcium carbonate, the inert particulateadditive having an average particle size of less than about ten microns.2. A polyester resin according to claim 1, comprising between about 40and 150 ppm of the inert particulate additive.
 3. A polyester resinaccording to claim 1, comprising between about 60 and 100 ppm of theinert particulate additive.
 4. A polyester resin according to claim 1,wherein the inert particulate additive has an average particle size ofless than about two microns.
 5. A polyester resin according to claim 1,wherein the inert particulate additive is surface-modified talc.
 6. Apolyester resin according to claim 5, wherein the surface-modified talcis talc treated with an organosilane coupling agent.
 7. A polyesterresin according to claim 1, wherein the inert particulate additive issurface-modified calcium carbonate.
 8. A polyester resin according toclaim 7, wherein the surface-modified calcium carbonate is calciumcarbonate treated with a stearic acid coupling agent.
 9. A polyesterpreform made from the polyester resin of claim
 1. 10. A polyestercontainer made from the polyester resin of claim
 1. 11. A polyesterresin that is capable of being formed into high-clarity bottlespossessing reduced coefficient of friction, the resin comprisingpolyethylene terephthalate and between about 40 and 100 ppm of an inertparticulate additive selected from the group consisting ofsurface-modified talc and surface-modified calcium carbonate, the inertparticulate additive having an average particle size of less than abouttwo microns.
 12. A method for making polyethylene terephthalate resinthat can be formed into high-clarity bottles possessing reducedcoefficient of friction, comprising: reacting a terephthalate componentand a diol component to form polyethylene terephthalate precursors;polymerizing the polyethylene terephthalate precursors via melt phasepolycondensation to form polymers of polyethylene terephthalate; andintroducing between about 20 and 200 ppm of an inert particulateadditive that is capable of reducing the coefficient of friction inbottles formed from the polyethylene terephthalate polymers; wherein theinert particulate additive is selected from the group consisting of talcand calcium carbonate; and wherein the inert particulate additive has anaverage particle size of less than about ten microns.
 13. A method formaking polyethylene terephthalate resin according to claim 12, whereinthe step of introducing an inert particulate additive comprisesintroducing between about 40 and 150 ppm of the inert particulateadditive.
 14. A method for making polyethylene terephthalate resinaccording to claim 12, wherein the step of introducing an inertparticulate additive comprises introducing between about 60 and 100 ppmof the inert particulate additive.
 15. A method for making polyethyleneterephthalate resin according to claim 12, wherein the step ofintroducing an inert particulate additive comprises introducingsurface-modified talc.
 16. A method for making polyethyleneterephthalate resin according to claim 12, wherein the step ofintroducing an inert particulate additive comprises introducingsurface-modified calcium carbonate.
 17. A method according to claim 12,wherein the step of reacting a terephthalate component and a diolcomponent comprises: reacting terephthalic acid and ethylene glycol in aheated esterification reaction to form monomers and oligomers ofterephthalic acid and ethylene glycol, as well as water; and removingwater as it is formed during the esterification reaction to enable theesterification reaction to go essentially to completion.
 18. A methodaccording to claim 12, wherein the step of reacting a terephthalatecomponent and a diol component comprises: reacting dimethylterephthalate and ethylene glycol in a heated ester exchange reaction toform monomers and oligomers of terephthalate and ethylene glycol, aswell as methanol; and removing methanol as it is formed during the esterexchange reaction to enable the ester exchange reaction to goessentially to completion.
 19. A method according to claim 12, furthercomprising: forming the polyethylene terephthalate polymers intopellets; and solid state polymerizing the polyethylene terephthalatepolymers.
 20. A method according to claim 12, further comprising formingthe polyethylene terephthalate polymers into preforms.
 21. A methodaccording to claim 20, further comprising forming the preforms intocontainers.
 22. A polyester container made according to the method ofclaim
 21. 23. A method according to claim 12, wherein the step ofintroducing an inert particulate additive comprises introducing anessentially dry, inert particulate additive into the polyethyleneterephthalate polymers after polycondensation.
 24. A method according toclaim 12, wherein the step of introducing an inert particulate additivefurther comprises introducing into the polyethylene terephthalatepolymers, after polycondensation, a reactive carrier having a molecularweight of less than about 10,000 g/mol, wherein the reactive carrier isa delivery vehicle for the inert particulate additive.
 25. A methodaccording to claim 24, wherein the step of introducing a reactivecarrier into the polyethylene terephthalate polymers comprises injectinga reactive carrier that is a liquid or slurry at near ambienttemperatures.
 26. A method according to claim 24, wherein the reactivecarrier is introduced to the polyethylene terephthalate polymers inquantities such that its concentration in the polymers is less thanabout 1000 ppm.
 27. A method according to claim 24, wherein the reactivecarrier comprises a polyol having a molecular weight that issufficiently high such the polyol will not substantially reduce theintrinsic viscosity of the polyethylene terephthalate polymer, and aviscosity that facilitates pumping of the polyol.
 28. A method accordingto claim 12, further comprising the step of introducing a UV absorberthat is capable of protecting the contents of packages formed from thepolyethylene terephthalate polymers.
 29. A polyester resin madeaccording to the process of claim
 12. 30. A method for makingpolyethylene terephthalate resin that can be formed into high-claritybottles possessing reduced coefficient of friction, comprising: reactingterephthalic acid and ethylene glycol in a heated esterificationreaction to form monomers and oligomers of terephthalic acid andethylene glycol; polymerizing the monomers and oligomers via melt phasepolycondensation to form polymers of polyethylene terephthalate;thereafter introducing via a reactive carrier between about 20 and 200ppm of an inert additive selected from the group consisting ofsurface-modified talc and surface-modified calcium carbonate, whereinthe reactive carrier is a polyol having a molecular weight that permitsthe polyol to be pumped at near ambient temperatures and wherein thereactive carrier is introduced to the polyethylene terephthalatepolymers in quantities such that bulk properties of the polyethyleneterephthalate polymers are not significantly affected; forming thepolyethylene terephthalate polymers into pellets; and solid statepolymerizing the polyethylene terephthalate polymers.
 31. A method formaking polyethylene terephthalate resin according to claim 30, whereinthe step of introducing an inert additive comprises introducing betweenabout 40 and 150 ppm of the inert additive.
 32. A method for makingpolyethylene terephthalate resin according to claim 30, wherein the stepof introducing an inert additive comprises introducing between about 60and 100 ppm of the inert additive.
 33. A method for making polyethyleneterephthalate resin according to claim 30, wherein the reactive carrieris introduced to the polyethylene terephthalate polymers in quantitiessuch that its concentration in the polymers is less than about 1000 ppm.34. A method according to claim 30, wherein the polyol reactive carrierhas a molecular weight of less than about 6000 g/mol.
 35. A methodaccording to claim 30, wherein the polyol reactive carrier has amolecular weight of less than about 4000 g/mol.
 36. A method accordingto claim 30, wherein the polyol reactive carrier has a molecular weightbetween about 300 and 2000 g/mol.
 37. A polyester resin made accordingto the process of claim
 30. 38. A polyester preform made according tothe process of claim
 30. 39. A polyester container made according to theprocess of claim 30.